Fabre Clément, Wei Xi, Sauvage Sabine, Le Thi Phuong Quynh, Ouillon Sylvain, Orange Didier, Herrmann Marine, Sánchez-Pérez José-Miguel
Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, CNRS, INPT, UPS, Avenue de l'Agrobiopole, 31326 Auzeville-Tolosane, France.
Laboratoire Ecologie Fonctionnelle et Environnement, Université de Toulouse, CNRS, INPT, UPS, Avenue de l'Agrobiopole, 31326 Auzeville-Tolosane, France.
Sci Total Environ. 2023 Dec 10;903:166589. doi: 10.1016/j.scitotenv.2023.166589. Epub 2023 Aug 25.
Fluvial organic carbon (OC) transfer is an essential resource for downstream ecosystems. Multiple factors affect its transfer process, e.g., climate or anthropogenic activities. Quantifying OC fluxes with fine spatiotemporal resolution is challenging in anthropised catchments. This study aims to quantify daily OC dynamics and to assess the impacts of short climate variability and damming on OC spatiotemporal transfer processes in a large tropical Asian river basin (the Red River) for an extended period (2003-2013) by combining empirical equations with modelling outputs. Firstly, empirical equations for calculating dissolved (DOC) and particulate OC (POC) concentrations were calibrated based on in-situ sampling data. Then, simulated daily discharge (Q) and suspended sediment concentrations were used to quantify daily OC fluxes. Results show that the parameters of the DOC and POC equations well represent the subbasins characteristics, underlining the effects of soil OC content, mean annual Q and Chlorophyll a. DOC and POC exports reached 222 and 406 kt yr at the basin outlet, accounting for 0.38 % of the total OC (TOC) exported by Asian rivers to the ocean. However, the specific yields of DOC (1.62 t km yr) and POC (2.96 t km yr) of the Red River basin were ~ 1.5 times those of other Asian basins. By comparing a reference scenario (without dams) to current conditions, we estimated 12 % and 88 % decreases in DOC and POC fluxes between 2008-2013 and 2003-2007, mainly due to damming. This study shows that climate variability may not impact OC dynamics in rivers as it explained <2 % of the variations. However, dam management, especially recent ones operating since 2008, deeply influences OC variations as the POC/TOC ratio decreased from 86 % to 47 %. Damming significantly decreased POC exports due to sediment retention, altering the equilibrium of OC cycling downstream, which may impact the food chain.
河流有机碳（OC）的输送是下游生态系统的重要资源。多种因素会影响其输送过程，例如气候或人类活动。在人为影响的集水区，以高时空分辨率量化OC通量具有挑战性。本研究旨在通过将经验方程与模型输出相结合，量化大型亚洲热带流域（红河）长期（2003 - 2013年）的每日OC动态，并评估短期气候变化和筑坝对OC时空输送过程的影响。首先，基于现场采样数据校准了计算溶解有机碳（DOC）和颗粒有机碳（POC）浓度的经验方程。然后，利用模拟的每日流量（Q）和悬浮泥沙浓度来量化每日OC通量。结果表明，DOC和POC方程的参数很好地代表了子流域特征，突出了土壤OC含量、年均流量Q和叶绿素a的影响。流域出口处的DOC和POC输出量分别达到222和406 kt/年，占亚洲河流向海洋输出的总有机碳（TOC）的0.38%。然而，红河流域DOC（1.62 t/km²/年）和POC（2.96 t/km²/年）的单位面积产量约为其他亚洲流域的1.5倍。通过将参考情景（无大坝）与当前状况进行比较，我们估计2008 - 2013年与2003 - 2007年相比，DOC和POC通量分别减少了12%和88%，主要原因是筑坝。本研究表明，气候变化对河流中OC动态的影响可能不大，因为其解释的变化小于2%。然而，大坝管理，尤其是2008年以来运行的近期大坝，对OC变化有深远影响，因为POC/TOC比值从86%降至47%。筑坝由于泥沙截留显著减少了POC输出，改变了下游OC循环的平衡，这可能影响食物链。
